Much of the western United States has been experiencing a historic and unrelenting drought, the worst in the region in centuries.

A study published in Nature Climate Change found the period from 2000 to 2021 was the driest in 1,200 years. Last year's drought severity was "exceptional," researchers said, and all indications are the extreme conditions will continue through 2022.

The human-caused climate crisis has made the megadrought 72% worse, the study noted.

On August 16, the federal government announced that starting in January the Colorado River will operate in a Tier 2 shortage condition for the first time, as the drought has taken a severe toll on the river and the nation's largest reservoirs -- Lake Mead and Lake Powell.

Amid the overuse of the river and the aridification of the region, the federal government is implementing mandatory water cuts and asking states to devise a plan to save the river basin. The Tier 2 shortage means Arizona, Nevada and Mexico will have to further reduce their Colorado River use.

Flames engulf a chair inside a burning home in Mariposa County, California, on July 23. The <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2022%2F07%2F27%2Fus%2Fgallery%2Foak-fire-california%2Findex.html" target="_blank">Oak Fire,</a> which started near Yosemite National Park, burned nearly 20,000 acres and is California's <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2022%2F07%2F26%2Fus%2Fcalifornia-oak-fire-yosemite-mariposa-county-tuesday%2Findex.html" target="_blank">biggest wildfire</a> of the year. The challenging terrain and abundant dry vegetation fueling the wildfire complicated efforts to tamp down its growth, a Cal Fire spokesperson told CNN.
Flames engulf a chair inside a burning home in Mariposa County, California, on July 23. The Oak Fire, which started near Yosemite National Park, burned nearly 20,000 acres and is California's biggest wildfire of the year. The challenging terrain and abundant dry vegetation fueling the wildfire complicated efforts to tamp down its growth, a Cal Fire spokesperson told CNN.
Noah Berger/AP
Craig Miller sits in his stranded houseboat at Lake Mead near Boulder City, Nevada, on June 23. Miller had been living on the stranded boat for over two weeks after engine trouble and falling lake levels left the boat above the water level.
Craig Miller sits in his stranded houseboat at Lake Mead near Boulder City, Nevada, on June 23. Miller had been living on the stranded boat for over two weeks after engine trouble and falling lake levels left the boat above the water level.
John Locher/AP
Some of the 20 hillside homes destroyed by the Coastal Fire are seen as cleanup work continues on June 17 in Laguna Niguel, California. <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2022%2F05%2F11%2Fweather%2Forange-county-california-fire-evacuations%2Findex.html" target="_blank">The May 11 brush fire</a> was fueled by windy and dry conditions amid California's severe drought, which has been compounded by climate change. Flames raced up the hill to reach the multimillion-dollar houses after the fire started below in a nearby canyon.
Some of the 20 hillside homes destroyed by the Coastal Fire are seen as cleanup work continues on June 17 in Laguna Niguel, California. The May 11 brush fire was fueled by windy and dry conditions amid California's severe drought, which has been compounded by climate change. Flames raced up the hill to reach the multimillion-dollar houses after the fire started below in a nearby canyon.
Mario Tama/Getty Images
Firefighters battle a brush fire at Coronado Pointe in Laguna Niguel, California, on May 11. Statewide, January to April were the driest first four months on record, the US Drought Monitor reported.
Firefighters battle a brush fire at Coronado Pointe in Laguna Niguel, California, on May 11. Statewide, January to April were the driest first four months on record, the US Drought Monitor reported.
Wally Skalij/Los Angeles Times/Getty Images
A formerly sunken boat sits on cracked earth hundreds of feet from what is now the shoreline on Lake Mead near Boulder City, Nevada, on May 9. According to a new projection from the Department of the Interior, Lake Mead's water level will be below 1,050 feet above sea level in January -- the threshold required to declare a <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2022%2F08%2F16%2Fus%2Fcolorado-river-water-cuts-lake-mead-negotiations-climate%2Findex.html" target="_blank">Tier 2 shortage</a> starting in 2023.
A formerly sunken boat sits on cracked earth hundreds of feet from what is now the shoreline on Lake Mead near Boulder City, Nevada, on May 9. According to a new projection from the Department of the Interior, Lake Mead's water level will be below 1,050 feet above sea level in January -- the threshold required to declare a Tier 2 shortage starting in 2023.
John Locher/AP
A dead fish lies on a section of dry lakebed along Lake Mead on May 9.
A dead fish lies on a section of dry lakebed along Lake Mead on May 9.
Mario Tama/Getty Images
Michelle Peters, a technical and compliance manager for Poseidon Water, walks through the reverse osmosis building at the Claude Lewis Carlsbad Desalination Plant in Carlsbad, California, on March 30. The plant converts ocean water into municipal water. In August, Gov. Gavin Newsom laid out a <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2Fus%2Flive-news%2Flake-mead-colorado-river-report%2Fh_8b9a61776c746ca11392b63b158381f6" target="_blank">multi-billion-dollar plan</a> to preserve the state's diminishing water supply for future years, which includes recycled water projects such as desalination of ocean water and salty water in groundwater basins.
Michelle Peters, a technical and compliance manager for Poseidon Water, walks through the reverse osmosis building at the Claude Lewis Carlsbad Desalination Plant in Carlsbad, California, on March 30. The plant converts ocean water into municipal water. In August, Gov. Gavin Newsom laid out a multi-billion-dollar plan to preserve the state's diminishing water supply for future years, which includes recycled water projects such as desalination of ocean water and salty water in groundwater basins.
Allen J. Schaben/Los Angeles Times/Getty Images
A landscaping crew removes non-functional turf from a residential development in Las Vegas on March 30. Under a Nevada state law passed last year, patches of non-functional grass that serve only for aesthetic purposes must be removed in favor of more desert-friendly landscaping.
A landscaping crew removes non-functional turf from a residential development in Las Vegas on March 30. Under a Nevada state law passed last year, patches of non-functional grass that serve only for aesthetic purposes must be removed in favor of more desert-friendly landscaping.
Joe Buglewicz/The New York Times/Redux
People walk on an area of Lake Powell that used to be underwater at Lone Rock Beach in Big Water, Utah, on March 27.
People walk on an area of Lake Powell that used to be underwater at Lone Rock Beach in Big Water, Utah, on March 27.
Justin Sullivan/Getty Images
The <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2021%2F07%2F17%2Fus%2Fgreat-salt-lake-drought-dying%2Findex.html" target="_blank">shrinking Great Salt Lake</a> is seen from Antelope Island State Park in Utah on March 15. Human water consumption and diversion have long depleted the lake. Scientists worry they're watching a slow-motion calamity unfold. Ten million birds flock to the Great Salt Lake each year to feed off of its now-struggling sea life, and more pelicans breed here than almost anywhere else in the country.
The shrinking Great Salt Lake is seen from Antelope Island State Park in Utah on March 15. Human water consumption and diversion have long depleted the lake. Scientists worry they're watching a slow-motion calamity unfold. Ten million birds flock to the Great Salt Lake each year to feed off of its now-struggling sea life, and more pelicans breed here than almost anywhere else in the country.
Bryan Tarnowski/The New York Times/Redux
In this GeoColor image from July 2021, smoke from numerous wildfires could be seen as gray-brown, in stark contrast to the white cloud cover over other parts of the continent.
In this GeoColor image from July 2021, smoke from numerous wildfires could be seen as gray-brown, in stark contrast to the white cloud cover over other parts of the continent.
NOAA
Visitors take photos in front of a thermometer in July 2021, at Death Valley National Park in Death Valley, California. Death Valley is known to be a hot place, but on July 9 <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2021%2F07%2F11%2Fweather%2Fweather-death-valley-heat-record-california-weekend%2Findex.html" target="_blank">it hit 130 degrees Fahrenheit</a> for only the fifth time in recorded history.
Visitors take photos in front of a thermometer in July 2021, at Death Valley National Park in Death Valley, California. Death Valley is known to be a hot place, but on July 9 it hit 130 degrees Fahrenheit for only the fifth time in recorded history.
Roger Kisby/The New York Times/Redux
These peaks of the Sierra Nevada mountain range, near Lone Pine, California, often have snow packs that last throughout the summer months. But there were none in July 2021.
These peaks of the Sierra Nevada mountain range, near Lone Pine, California, often have snow packs that last throughout the summer months. But there were none in July 2021.
David McNew/Getty Images
Golden Davis cools off in a mister along the Las Vegas Strip on July 9, 2021. The city tied its all-time temperature record of 117 degrees Fahrenheit over the weekend.
Golden Davis cools off in a mister along the Las Vegas Strip on July 9, 2021. The city tied its all-time temperature record of 117 degrees Fahrenheit over the weekend.
John Locher/AP
A utility crew works on power lines in July 2021, in front of a hillside that was burned by the Salt Fire in California's Shasta County.
A utility crew works on power lines in July 2021, in front of a hillside that was burned by the Salt Fire in California's Shasta County.
Josh Edelson/AFP/Getty Images
Annette Garcia, director of the Coachella Valley Horse Rescue, straps ice packs onto a horse's legs to help keep him cool amid a water shortage in Indio, California, in July 2021.
Annette Garcia, director of the Coachella Valley Horse Rescue, straps ice packs onto a horse's legs to help keep him cool amid a water shortage in Indio, California, in July 2021.
Mario Tama/Getty Images
This aerial photo shows houseboats anchored at the Bidwell Canyon Marina in Oroville, California, in June 2021. As water levels continued to fall at Lake Oroville, officials were flagging houseboats for removal so they could avoid being stuck or damaged.
This aerial photo shows houseboats anchored at the Bidwell Canyon Marina in Oroville, California, in June 2021. As water levels continued to fall at Lake Oroville, officials were flagging houseboats for removal so they could avoid being stuck or damaged.
Justin Sullivan/Getty Images
People in Portland, Oregon, cool off at the Oregon Convention Center on Sunday, June 27, 2021. Portland <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2021%2F06%2F28%2Fweather%2Fheat-waves-west-coast-records%2Findex.html" target="_blank">set an all-time high of 112 degrees</a> that day. It surpassed it a day later with a high of 116.
People in Portland, Oregon, cool off at the Oregon Convention Center on Sunday, June 27, 2021. Portland set an all-time high of 112 degrees that day. It surpassed it a day later with a high of 116.
Nathan Howard/Getty Images
Park visitors in Big Water, Utah, walk on an area of Lake Powell that used to be underwater at Lone Rock Beach in June 2021.
Park visitors in Big Water, Utah, walk on an area of Lake Powell that used to be underwater at Lone Rock Beach in June 2021.
Justin Sullivan/Getty Images
The exposed lake bed of the San Gabriel Reservoir is seen near Azusa, California, in June 2021.
The exposed lake bed of the San Gabriel Reservoir is seen near Azusa, California, in June 2021.
Mario Tama/Getty Images
Ranchers Jim Jensen, center, and Bill Jensen inspect a trench they are working on to try to get more water to their ranch in Tomales, California, in June 2021. As the drought continues in California, many ranchers and farmers are beginning to see their wells and ponds dry up. They are having to make modifications to their existing water resources or have water trucked in for their livestock.
Ranchers Jim Jensen, center, and Bill Jensen inspect a trench they are working on to try to get more water to their ranch in Tomales, California, in June 2021. As the drought continues in California, many ranchers and farmers are beginning to see their wells and ponds dry up. They are having to make modifications to their existing water resources or have water trucked in for their livestock.
Justin Sullivan/Getty Images
California's Tule Lake National Wildlife Refuge, near the Oregon border, is seen in May 2021. The area has been severely affected by drought and the lack of irrigation waters from Upper Klamath Lake, which usually feeds into the refuge.
California's Tule Lake National Wildlife Refuge, near the Oregon border, is seen in May 2021. The area has been severely affected by drought and the lack of irrigation waters from Upper Klamath Lake, which usually feeds into the refuge.
Will Matsuda/The New York Times/Redux
Firefighters battle a brushfire in Santa Barbara, California, in May 2021.
Firefighters battle a brushfire in Santa Barbara, California, in May 2021.
AP
This aerial photo shows rows of almond trees sitting on the ground during an orchard removal project in Snelling, California, in May 2021. Because of a shortage of water in the Central Valley, some farmers are having to remove crops that require excessive watering.
This aerial photo shows rows of almond trees sitting on the ground during an orchard removal project in Snelling, California, in May 2021. Because of a shortage of water in the Central Valley, some farmers are having to remove crops that require excessive watering.
Justin Sullivan/Getty Images